Rate Adaptation Using Network Signaling

ABSTRACT

Systems, methods, and instrumentalities are disclosed to perform rate adaptation in a wireless transmit/receive unit (WTRU). The WTRU may receive an encoded data stream, which may be encoded according to a Dynamic Adaptive HTTP Streaming (DASH) standard. The WTRU may request and/or receive the data stream from a content server. The WTRU may monitor and/or receive a cross-layer parameter, such as a physical layer parameter, a RRC layer parameter, and/or a MAC layer parameter (e.g., a CQI, a PRB allocation, a MRM, or the like). The WTRU may perform rate adaption based on the cross-layer parameter. For example, the WTRU may set the CE bit of an Explicit Congestion Notification (ECN) field based on the cross-layer parameter. The WTRU may determine to request the data stream encoded at a different rate based on the cross-layer parameter, the CE bit, and/or a prediction based on the cross-layer parameter.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional PatentApplication No. 61/680,206, filed Aug. 6, 2012, the contents of whichare hereby incorporated by reference herein.

BACKGROUND

MPEG/3GPP Dynamic Adaptive HTTP Streaming (DASH) standard may define aframework for design of bandwidth-adaptive delivery of streaming contentover wireless and wired networks. DASH may be a pull-based streamingparadigm where the client may play a central role in carrying theintelligence that drives the video adaptation.

SUMMARY

A wireless transmit/receive unit (WTRU) may perform rate adaptation. TheWTRU may include an adaptive bitrate client, such as a DASH client, forexample, residing at the application layer of the WTRU. The WTRU mayreceive an encoded data stream. The data stream may be a video stream,for example. The data stream may be a multi-rate encoded data stream.For example, the data stream may be encoded according to a DynamicAdaptive HTTP Streaming (DASH) standard. The WTRU may request and/orreceive the data stream encoded at a first rate. For example, the WTRUmay request and/or receive (e.g., indirectly receive) the data streamfrom a content server, such as a HTTP content server, or the like.

The WTRU may perform rate adaption, for example, according to across-layer parameter and/or a congestion encountered (CE) bit. Rateadaption may be performed at the application layer of the WTRU. Forexample, rate adaption may include requesting the data stream encoded ata different rate, issuing TCP reset associated with the data stream,and/or aborting an HTTP request for the data stream.

The WTRU may monitor and/or receive a cross-layer parameter. Across-layer parameter may be any parameters (e.g., signaling) that isavailable at a layer of a WTRU and/or directed to a layer of the WTRUother than the application layer. For example, the cross-layer parametermay be a physical layer parameter, a RRC layer parameter, and/or a MAClayer parameter. For example, the cross-layer parameters may be a CQI, aPRB allocation, a MRM, or the like.

The WTRU may perform rate adaption based on the cross-layer parameter.For example, the WTRU may set the CE bit of an Explicit CongestionNotification (ECN) field based on the cross-layer parameter. The WTRUmay set and/or receive a CE bit of an ECN field based on the cross-layerparameter. The WTRU may predict and/or estimate one or more of networkcongestion, throughout of the communication channel, a cell change event(e.g., a mobility event), and/or a channel condition that indicates lossof throughput using the cross-layer parameter. For example, the WTRU maydetermine to request the data stream encoded at a second rate based onone or more of the cross-layer parameter, the CE bit, and/or theprediction based on the cross-layer parameter. The second rate may belower than the first rate or the second rate may be higher than thefirst rate. The WTRU may receive the data stream encoded at the secondrate.

The WTRU may receive a congestion encountered (CE) bit. The CE bit maybe part of an ECN field. The ECN field may be received from a networkelement, such as a router, eNodeB, gateway, or the like. The WTRU mayreceive the CE bit upon a network element detecting one or more of acongestion scenario, a cell change event (e.g., a mobility event),and/or a channel condition that indicates loss of throughput. The WTRUmay determine to request the data stream encoded at a different ratebased on the CE bit.

The WTRU may monitor a PDCCH and determine a physical layer parameterbased on the PDCCH. For example, the physical layer parameter mayinclude a CQI, a PRB allocation, or the like. The WTRU may determine torequest the data stream encoded at a different rate based on thephysical layer parameter. For example, the WTRU may set the CE bit of anECN field based on the physical layer parameters, and determine torequest the data stream encoded at the different rate based on the CEbit. The WTRU may request and/or receive the data stream encoded at adifferent rate based on the CE bit.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a system diagram of an example communications system in whichone or more disclosed embodiments may be implemented.

FIG. 1B is a system diagram of an example wireless transmit/receive unit(WTRU) that may be used within the communications system illustrated inFIG. 1A.

FIG. 1C is a system diagram of an example radio access network and anexample core network that may be used within the communications systemillustrated in FIG. 1A.

FIG. 1D is a system diagram of another example radio access network andanother example core network that may be used within the communicationssystem illustrated in FIG. 1A.

FIG. 1E is a system diagram of another example radio access network andanother example core network that may be used within the communicationssystem illustrated in FIG. 1A.

FIG. 2 is a diagram that illustrates an example of a wireless systemwith a DASH streaming client.

FIG. 3A is a diagram illustrating an example method of ExplicitCongestion Notification (ECN) usage where an IP packet may betransmitted from a network element.

FIG. 3B is a diagram illustrating an example method of ECN usage forDASH.

FIG. 4 is a diagram illustrating an example of an ECN bit that may beset by a network element and used by a WTRU for rate adaptation.

FIG. 5 is a flow diagram illustrating an example procedure for a networkelement to set the ECN bit and for a WTRU to perform rate adaptation.

FIG. 6 is a diagram illustrating an example of a time lines for clientrate adaptation and estimate throughput.

FIG. 7 is a diagram illustrating an example of cross-layer DASH rateadaptation.

FIG. 8 is a diagram illustrating an example use of Radio ResourceControl (RRC) signaling for client rate adaptation.

FIG. 9 is a diagram illustrating an example of Transmission ControlProtocol (TCP) congestion window size behavior vs. time.

FIG. 10 is a diagram illustrating example timing of Hypertext TransferProtocol (HTTP) GET requests and available bandwidth vs. time.

FIG. 11 is a diagram illustrating an example of the estimated availablebandwidth by TCP as a function of time.

DETAILED DESCRIPTION

A detailed description of illustrative embodiments will now be describedwith reference to the various Figures. Although this descriptionprovides a detailed example of possible implementations, it should benoted that the details are intended to be exemplary and in no way limitthe scope of the application.

FIG. 1A is a diagram of an example communications system 100 in whichone or more disclosed embodiments may be implemented. The communicationssystem 100 may be a multiple access system that provides content, suchas voice, data, video, messaging, broadcast, etc., to multiple wirelessusers. The communications system 100 may enable multiple wireless usersto access such content through the sharing of system resources,including wireless bandwidth. For example, the communications systems100 may employ one or more channel access methods, such as code divisionmultiple access (CDMA), time division multiple access (TDMA), frequencydivision multiple access (FDMA), orthogonal FDMA (OFDMA), single-carrierFDMA (SC-FDMA), and the like.

As shown in FIG. 1A, the communications system 100 may include wirelesstransmit/receive units (WTRUs) 102 a, 102 b, 102 c, and/or 102 d (whichgenerally or collectively may be referred to as WTRU 102), a radioaccess network (RAN) 103/104/105, a core network 106/107/109, a publicswitched telephone network (PSTN) 108, the Internet 110, and othernetworks 112, though it will be appreciated that the disclosedembodiments contemplate any number of WTRUs, base stations, networks,and/or network elements. Each of the WTRUs 102 a, 102 b, 102 c, 102 dmay be any type of device configured to operate and/or communicate in awireless environment. By way of example, the WTRUs 102 a, 102 b, 102 c,102 d may be configured to transmit and/or receive wireless signals andmay include user equipment (UE), a mobile station, a fixed or mobilesubscriber unit, a pager, a cellular telephone, a personal digitalassistant (PDA), a smartphone, a laptop, a netbook, a personal computer,a wireless sensor, consumer electronics, and the like.

The communications systems 100 may also include a base station 114 a anda base station 114 b. Each of the base stations 114 a, 114 b may be anytype of device configured to wirelessly interface with at least one ofthe WTRUs 102 a, 102 b, 102 c, 102 d to facilitate access to one or morecommunication networks, such as the core network 106/107/109, theInternet 110, and/or the networks 112. By way of example, the basestations 114 a, 114 b may be a base transceiver station (BTS), a Node-B,an eNode B, a Home Node B, a Home eNode B, a site controller, an accesspoint (AP), a wireless router, and the like. While the base stations 114a, 114 b are each depicted as a single element, it will be appreciatedthat the base stations 114 a, 114 b may include any number ofinterconnected base stations and/or network elements.

The base station 114 a may be part of the RAN 103/104/105, which mayalso include other base stations and/or network elements (not shown),such as a base station controller (BSC), a radio network controller(RNC), relay nodes, etc. The base station 114 a and/or the base station114 b may be configured to transmit and/or receive wireless signalswithin a particular geographic region, which may be referred to as acell (not shown). The cell may further be divided into cell sectors. Forexample, the cell associated with the base station 114 a may be dividedinto three sectors. Thus, in one embodiment, the base station 114 a mayinclude three transceivers, e.g., one for each sector of the cell. Inanother embodiment, the base station 114 a may employ multiple-inputmultiple output (MIMO) technology and, therefore, may utilize multipletransceivers for each sector of the cell.

The base stations 114 a, 114 b may communicate with one or more of theWTRUs 102 a, 102 b, 102 c, 102 d over an air interface 115/116/117,which may be any suitable wireless communication link (e.g., radiofrequency (RF), microwave, infrared (IR), ultraviolet (UV), visiblelight, etc.). The air interface 115/116/117 may be established using anysuitable radio access technology (RAT).

More specifically, as noted above, the communications system 100 may bea multiple access system and may employ one or more channel accessschemes, such as CDMA, TDMA, FDMA, OFDMA, SC-FDMA, and the like. Forexample, the base station 114 a in the RAN 103/104/105 and the WTRUs 102a, 102 b, 102 c may implement a radio technology such as UniversalMobile Telecommunications System (UMTS) Terrestrial Radio Access (UTRA),which may establish the air interface 115/116/117 using wideband CDMA(WCDMA). WCDMA may include communication protocols such as High-SpeedPacket Access (HSPA) and/or Evolved HSPA (HSPA±). HSPA may includeHigh-Speed Downlink Packet Access (HSDPA) and/or High-Speed UplinkPacket Access (HSDPA).

In another embodiment, the base station 114 a and the WTRUs 102 a, 102b, 102 c may implement a radio technology such as Evolved UNITSTerrestrial Radio Access (E-UTRA), which may establish the air interface115/116/117 using Long Term Evolution (LTE) and/or LTE-Advanced (LTE-A).

In other embodiments, the base station 114 a and the WTRUs 102 a, 102 b,102 c may implement radio technologies such as IEEE 802.16 (e.g.,Worldwide Interoperability for Microwave Access (WiMAX)), CDMA2000,CDMA2000 1×, CDMA2000 EV-DO, Interim Standard 2000 (IS-2000), InterimStandard 95 (IS-95), Interim Standard 856 (IS-856), Global System forMobile communications (GSM), Enhanced Data rates for GSM Evolution(EDGE), GSM EDGE (GERAN), and the like.

The base station 114 b in FIG. 1A may be a wireless router, Home Node B,Home eNode B, or access point, for example, and may utilize any suitableRAT for facilitating wireless connectivity in a localized area, such asa place of business, a home, a vehicle, a campus, and the like. In oneembodiment, the base station 114 b and the WTRUs 102 c, 102 d mayimplement a radio technology such as IEEE 802.11 to establish a wirelesslocal area network (WLAN). In another embodiment, the base station 114 band the WTRUs 102 c, 102 d may implement a radio technology such as IEEE802.15 to establish a wireless personal area network (WPAN). In yetanother embodiment, the base station 114 b and the WTRUs 102 c, 102 dmay utilize a cellular-based RAT (e.g., WCDMA, CDMA2000, GSM, LTE,LTE-A, etc.) to establish a picocell or femtocell. As shown in FIG. 1A,the base station 114 b may have a direct connection to the Internet 110.Thus, the base station 114 b may not be required to access the Internet110 via the core network 106/107/109.

The RAN 103/104/105 may be in communication with the core network106/107/109, which may be any type of network configured to providevoice, data, applications, and/or voice over internet protocol (VoIP)services to one or more of the WTRUs 102 a, 102 b, 102 c, 102 d. Forexample, the core network 106/107/109 may provide call control, billingservices, mobile location-based services, pre-paid calling, Internetconnectivity, video distribution, etc., and/or perform high-levelsecurity functions, such as user authentication. Although not shown inFIG. 1A, it will be appreciated that the RAN 103/104/105 and/or the corenetwork 106/107/109 may be in direct or indirect communication withother RANs that employ the same RAT as the RAN 103/104/105 or adifferent RAT. For example, in addition to being connected to the RAN103/104/105, which may be utilizing an E-UTRA radio technology, the corenetwork 106/107/109 may also be in communication with another RAN (notshown) employing a GSM radio technology.

The core network 106/107/109 may also serve as a gateway for the WTRUs102 a, 102 b, 102 c, 102 d to access the PSTN 108, the Internet 110,and/or other networks 112. The PSTN 108 may include circuit-switchedtelephone networks that provide plain old telephone service (POTS). TheInternet 110 may include a global system of interconnected computernetworks and devices that use common communication protocols, such asthe transmission control protocol (TCP), user datagram protocol (UDP)and the internet protocol (IP) in the TCP/IP internet protocol suite.The networks 112 may include wired or wireless communications networksowned and/or operated by other service providers. For example, thenetworks 112 may include another core network connected to one or moreRANs, which may employ the same RAT as the RAN 103/104/105 or adifferent RAT.

Some or all of the WTRUs 102 a, 102 b, 102 c, 102 d in thecommunications system 100 may include multi-mode capabilities, e.g., theWTRUs 102 a, 102 b, 102 c, 102 d may include multiple transceivers forcommunicating with different wireless networks over different wirelesslinks. For example, the WTRU 102 c shown in FIG. 1A may be configured tocommunicate with the base station 114 a, which may employ acellular-based radio technology, and with the base station 114 b, whichmay employ an IEEE 802 radio technology.

FIG. 1B is a system diagram of an example WTRU 102. As shown in FIG. 1B,the WTRU 102 may include a processor 118, a transceiver 120, atransmit/receive element 122, a speaker/microphone 124, a keypad 126, adisplay/touchpad 128, non-removable memory 130, removable memory 132, apower source 134, a global positioning system (GPS) chipset 136, andother peripherals 138. It will be appreciated that the WTRU 102 mayinclude any sub-combination of the foregoing elements while remainingconsistent with an embodiment. Also, embodiments contemplate that thebase stations 114 a and 114 b, and/or the nodes that base stations 114 aand 114 b may represent, such as but not limited to transceiver station(BTS), a Node-B, a site controller, an access point (AP), a home node-B,an evolved home node-B (eNodeB), a home evolved node-B (HeNB), a homeevolved node-B gateway, and proxy nodes, among others, may include someor all of the elements depicted in FIG. 1B and described herein.

The processor 118 may be a general purpose processor, a special purposeprocessor, a conventional processor, a digital signal processor (DSP), aplurality of microprocessors, one or more microprocessors in associationwith a DSP core, a controller, a microcontroller, Application SpecificIntegrated Circuits (ASICs), Field Programmable Gate Array (FPGAs)circuits, any other type of integrated circuit (IC), a state machine,and the like. The processor 118 may perform signal coding, dataprocessing, power control, input/output processing, and/or any otherfunctionality that enables the WTRU 102 to operate in a wirelessenvironment. The processor 118 may be coupled to the transceiver 120,which may be coupled to the transmit/receive element 122. While FIG. 1Bdepicts the processor 118 and the transceiver 120 as separatecomponents, it will be appreciated that the processor 118 and thetransceiver 120 may be integrated together in an electronic package orchip.

The transmit/receive element 122 may be configured to transmit signalsto, or receive signals from, a base station (e.g., the base station 114a) over the air interface 115/116/117. For example, in one embodiment,the transmit/receive element 122 may be an antenna configured totransmit and/or receive RF signals. In another embodiment, thetransmit/receive element 122 may be an emitter/detector configured totransmit and/or receive IR, UV, or visible light signals, for example.In yet another embodiment, the transmit/receive element 122 may beconfigured to transmit and receive both RF and light signals. It will beappreciated that the transmit/receive element 122 may be configured totransmit and/or receive any combination of wireless signals.

In addition, although the transmit/receive element 122 is depicted inFIG. 1B as a single element, the WTRU 102 may include any number oftransmit/receive elements 122. More specifically, the WTRU 102 mayemploy MIMO technology. Thus, in one embodiment, the WTRU 102 mayinclude two or more transmit/receive elements 122 (e.g., multipleantennas) for transmitting and receiving wireless signals over the airinterface 115/116/117.

The transceiver 120 may be configured to modulate the signals that areto be transmitted by the transmit/receive element 122 and to demodulatethe signals that are received by the transmit/receive element 122. Asnoted above, the WTRU 102 may have multi-mode capabilities. Thus, thetransceiver 120 may include multiple transceivers for enabling the WTRU102 to communicate via multiple RATs, such as UTRA and IEEE 802.11, forexample.

The processor 118 of the WTRU 102 may be coupled to, and may receiveuser input data from, the speaker/microphone 124, the keypad 126, and/orthe display/touchpad 128 (e.g., a liquid crystal display (LCD) displayunit or organic light-emitting diode (OLED) display unit). The processor118 may also output user data to the speaker/microphone 124, the keypad126, and/or the display/touchpad 128. In addition, the processor 118 mayaccess information from, and store data in, any type of suitable memory,such as the non-removable memory 130 and/or the removable memory 132.The non-removable memory 130 may include random-access memory (RAM),read-only memory (ROM), a hard disk, or any other type of memory storagedevice. The removable memory 132 may include a subscriber identitymodule (SIM) card, a memory stick, a secure digital (SD) memory card,and the like. In other embodiments, the processor 118 may accessinformation from, and store data in, memory that is not physicallylocated on the WTRU 102, such as on a server or a home computer (notshown).

The processor 118 may receive power from the power source 134, and maybe configured to distribute and/or control the power to the othercomponents in the WTRU 102. The power source 134 may be any suitabledevice for powering the WTRU 102. For example, the power source 134 mayinclude one or more dry cell batteries (e.g., nickel-cadmium (NiCd),nickel-zinc (NiZn), nickel metal hydride (NiMH), lithium-ion (Li-ion),etc.), solar cells, fuel cells, and the like.

The processor 118 may also be coupled to the GPS chipset 136, which maybe configured to provide location information (e.g., longitude andlatitude) regarding the current location of the WTRU 102. In additionto, or in lieu of, the information from the GPS chipset 136, the WTRU102 may receive location information over the air interface 115/116/117from a base station (e.g., base stations 114 a, 114 b) and/or determineits location based on the timing of the signals being received from twoor more nearby base stations. It will be appreciated that the WTRU 102may acquire location information by way of any suitablelocation-determination method while remaining consistent with anembodiment.

The processor 118 may further be coupled to other peripherals 138, whichmay include one or more software and/or hardware modules that provideadditional features, functionality and/or wired or wirelessconnectivity. For example, the peripherals 138 may include anaccelerometer, an e-compass, a satellite transceiver, a digital camera(for photographs or video), a universal serial bus (USB) port, avibration device, a television transceiver, a hands free headset, aBluetooth® module, a frequency modulated (FM) radio unit, a digitalmusic player, a media player, a video game player module, an Internetbrowser, and the like.

FIG. 1C is a system diagram of the RAN 103 and the core network 106according to an embodiment. As noted above, the RAN 103 may employ aUTRA radio technology to communicate with the WTRUs 102 a, 102 b, 102 cover the air interface 115. The RAN 103 may also be in communicationwith the core network 106. As shown in FIG. 1C, the RAN 103 may includeNode-Bs 140 a, 140 b, 140 c, which may each include one or moretransceivers for communicating with the WTRUs 102 a, 102 b, 102 c overthe air interface 115. The Node-Bs 140 a, 140 b, 140 c may each beassociated with a particular cell (not shown) within the RAN 103. TheRAN 103 may also include RNCs 142 a, 142 b. It will be appreciated thatthe RAN 103 may include any number of Node-Bs and RNCs while remainingconsistent with an embodiment.

As shown in FIG. 1C, the Node-Bs 140 a, 140 b may be in communicationwith the RNC 142 a. Additionally, the Node-B 140 c may be incommunication with the RNC 142 b. The Node-Bs 140 a, 140 b, 140 c maycommunicate with the respective RNCs 142 a, 142 b via an Iub interface.The RNCs 142 a, 142 b may be in communication with one another via anIur interface. Each of the RNCs 142 a, 142 b may be configured tocontrol the respective Node-Bs 140 a, 140 b, 140 c to which it isconnected. In addition, each of the RNCs 142 a, 142 b may be configuredto carry out or support other functionality, such as outer loop powercontrol, load control, admission control, packet scheduling, handovercontrol, macrodiversity, security functions, data encryption, and thelike.

The core network 106 shown in FIG. 1C may include a media gateway (MGW)144, a mobile switching center (MSC) 146, a serving GPRS support node(SGSN) 148, and/or a gateway GPRS support node (GGSN) 150. While each ofthe foregoing elements are depicted as part of the core network 106, itwill be appreciated that any one of these elements may be owned and/oroperated by an entity other than the core network operator.

The RNC 142 a in the RAN 103 may be connected to the MSC 146 in the corenetwork 106 via an IuCS interface. The MSC 146 may be connected to theMGW 144. The MSC 146 and the MGW 144 may provide the WTRUs 102 a, 102 b,102 c with access to circuit-switched networks, such as the PSTN 108, tofacilitate communications between the WTRUs 102 a, 102 b, 102 c andtraditional land-line communications devices.

The RNC 142 a in the RAN 103 may also be connected to the SGSN 148 inthe core network 106 via an IuPS interface. The SGSN 148 may beconnected to the GGSN 150. The SGSN 148 and the GGSN 150 may provide theWTRUs 102 a, 102 b, 102 c with access to packet-switched networks, suchas the Internet 110, to facilitate communications between and the WTRUs102 a, 102 b, 102 c and IP-enabled devices.

As noted above, the core network 106 may also be connected to thenetworks 112, which may include other wired or wireless networks thatare owned and/or operated by other service providers.

FIG. 1D is a system diagram of the RAN 104 and the core network 107according to an embodiment. As noted above, the RAN 104 may employ anE-UTRA radio technology to communicate with the WTRUs 102 a, 102 b, 102c over the air interface 116. The RAN 104 may also be in communicationwith the core network 107.

The RAN 104 may include eNode-Bs 160 a, 160 b, 160 c, though it will beappreciated that the RAN 104 may include any number of eNode-Bs whileremaining consistent with an embodiment. The eNode-Bs 160 a, 160 b, 160c may each include one or more transceivers for communicating with theWTRUs 102 a, 102 b, 102 c over the air interface 116. In one embodiment,the eNode-Bs 160 a, 160 b, 160 c may implement MIMO technology. Thus,the eNode-B 160 a, for example, may use multiple antennas to transmitwireless signals to, and receive wireless signals from, the WTRU 102 a.

Each of the eNode-Bs 160 a, 160 b, 160 c may be associated with aparticular cell (not shown) and may be configured to handle radioresource management decisions, handover decisions, scheduling of usersin the uplink and/or downlink, and the like. As shown in FIG. 1D, theeNode-Bs 160 a, 160 b, 160 c may communicate with one another over an X2interface.

The core network 107 shown in FIG. 1D may include a mobility managementgateway (MME) 162, a serving gateway 164, and a packet data network(PDN) gateway 166. While each of the foregoing elements are depicted aspart of the core network 107, it will be appreciated that any one ofthese elements may be owned and/or operated by an entity other than thecore network operator.

The MME 162 may be connected to each of the eNode-Bs 160 a, 160 b, 160 cin the RAN 104 via an S1 interface and may serve as a control node. Forexample, the MME 162 may be responsible for authenticating users of theWTRUs 102 a, 102 b, 102 c, bearer activation/deactivation, selecting aparticular serving gateway during an initial attach of the WTRUs 102 a,102 b, 102 c, and the like. The MME 162 may also provide a control planefunction for switching between the RAN 104 and other RANs (not shown)that employ other radio technologies, such as GSM or WCDMA.

The serving gateway 164 may be connected to each of the eNode-Bs 160 a,160 b, 160 c in the RAN 104 via the S1 interface. The serving gateway164 may generally route and forward user data packets to/from the WTRUs102 a, 102 b, 102 c. The serving gateway 164 may also perform otherfunctions, such as anchoring user planes during inter-eNode B handovers,triggering paging when downlink data is available for the WTRUs 102 a,102 b, 102 c, managing and storing contexts of the WTRUs 102 a, 102 b,102 c, and the like.

The serving gateway 164 may also be connected to the PDN gateway 166,which may provide the WTRUs 102 a, 102 b, 102 c with access topacket-switched networks, such as the Internet 110, to facilitatecommunications between the WTRUs 102 a, 102 b, 102 c and IP-enableddevices.

The core network 107 may facilitate communications with other networks.For example, the core network 107 may provide the WTRUs 102 a, 102 b,102 c with access to circuit-switched networks, such as the PSTN 108, tofacilitate communications between the WTRUs 102 a, 102 b, 102 c andtraditional land-line communications devices. For example, the corenetwork 107 may include, or may communicate with, an IP gateway (e.g.,an IP multimedia subsystem (IMS) server) that serves as an interfacebetween the core network 107 and the PSTN 108. In addition, the corenetwork 107 may provide the WTRUs 102 a, 102 b, 102 c with access to thenetworks 112, which may include other wired or wireless networks thatare owned and/or operated by other service providers.

FIG. 1E is a system diagram of the RAN 105 and the core network 109according to an embodiment. The RAN 105 may be an access service network(ASN) that employs IEEE 802.16 radio technology to communicate with theWTRUs 102 a, 102 b, 102 c over the air interface 117. As will be furtherdiscussed below, the communication links between the differentfunctional entities of the WTRUs 102 a, 102 b, 102 c, the RAN 105, andthe core network 109 may be defined as reference points.

As shown in FIG. 1E, the RAN 105 may include base stations 180 a, 180 b,180 c, and an ASN gateway 182, though it will be appreciated that theRAN 105 may include any number of base stations and ASN gateways whileremaining consistent with an embodiment. The base stations 180 a, 180 b,180 c may each be associated with a particular cell (not shown) in theRAN 105 and may each include one or more transceivers for communicatingwith the WTRUs 102 a, 102 b, 102 c over the air interface 117. In oneembodiment, the base stations 180 a, 180 b, 180 c may implement MIMOtechnology. Thus, the base station 180 a, for example, may use multipleantennas to transmit wireless signals to, and receive wireless signalsfrom, the WTRU 102 a. The base stations 180 a, 180 b, 180 c may alsoprovide mobility management functions, such as handoff triggering,tunnel establishment, radio resource management, traffic classification,quality of service (QoS) policy enforcement, and the like. The ASNgateway 182 may serve as a traffic aggregation point and may beresponsible for paging, caching of subscriber profiles, routing to thecore network 109, and the like.

The air interface 117 between the WTRUs 102 a, 102 b, 102 c and the RAN105 may be defined as an R1 reference point that implements the IEEE802.16 specification. In addition, each of the WTRUs 102 a, 102 b, 102 cmay establish a logical interface (not shown) with the core network 109.The logical interface between the WTRUs 102 a, 102 b, 102 c and the corenetwork 109 may be defined as an R2 reference point, which may be usedfor authentication, authorization, IP host configuration management,and/or mobility management.

The communication link between each of the base stations 180 a, 180 b,180 c may be defined as an R8 reference point that includes protocolsfor facilitating WTRU handovers and the transfer of data between basestations. The communication link between the base stations 180 a, 180 b,180 c and the ASN gateway 182 may be defined as an R6 reference point.The R6 reference point may include protocols for facilitating mobilitymanagement based on mobility events associated with each of the WTRUs102 a, 102 b, 102 c.

As shown in FIG. 1E, the RAN 105 may be connected to the core network109. The communication link between the RAN 105 and the core network 109may defined as an R3 reference point that includes protocols forfacilitating data transfer and mobility management capabilities, forexample. The core network 109 may include a mobile IP home agent(MIP-HA) 184, an authentication, authorization, accounting (AAA) server186, and a gateway 188. While each of the foregoing elements aredepicted as part of the core network 109, it will be appreciated thatany one of these elements may be owned and/or operated by an entityother than the core network operator.

The MIP-HA may be responsible for IP address management, and may enablethe WTRUs 102 a, 102 b, 102 c to roam between different ASNs and/ordifferent core networks. The MIP-HA 184 may provide the WTRUs 102 a, 102b, 102 c with access to packet-switched networks, such as the Internet110, to facilitate communications between the WTRUs 102 a, 102 b, 102 cand IP-enabled devices. The AAA server 186 may be responsible for userauthentication and for supporting user services. The gateway 188 mayfacilitate interworking with other networks. For example, the gateway188 may provide the WTRUs 102 a, 102 b, 102 c with access tocircuit-switched networks, such as the PSTN 108, to facilitatecommunications between the WTRUs 102 a, 102 b, 102 c and traditionalland-line communications devices. In addition, the gateway 188 mayprovide the WTRUs 102 a, 102 b, 102 c with access to the networks 112,which may include other wired or wireless networks that are owned and/oroperated by other service providers.

Although not shown in FIG. 1E, it will be appreciated that the RAN 105may be connected to other ASNs and the core network 109 may be connectedto other core networks. The communication link between the RAN 105 theother ASNs may be defined as an R4 reference point, which may includeprotocols for coordinating the mobility of the WTRUs 102 a, 102 b, 102 cbetween the RAN 105 and the other ASNs. The communication link betweenthe core network 109 and the other core networks may be defined as an R5reference, which may include protocols for facilitating interworkingbetween home core networks and visited core networks.

Rate adaptation (e.g., DASH rate adaptation), for example, rate adaptioncontrolled by a WTRU may be provided. Rate adaptation may be enabledusing network signaling. Cross layer signaling in the WTRU may beprovided to enable rate adaptation. For example, a DASH client in a WTRUmay be informed of the congestion level of the network and the state ofwireless channel. The client may use this information to perform networkrate adaptation, which may improve, for example, the user's Quality ofExperience (QoE). For example, the client may receive an indication ofrate and/or latency changes earlier than the client may by monitoringtransport layer statistics.

A client may be provided with some or all of the intelligence relatingto rate adaption, for example, in a pull-based streaming paradigm. Theclient may be expected to estimate the available network bandwidth. Theclient may request media segments encoded at appropriate rates, forexample, according to the available network bandwidth. The client'sability to estimate bandwidth may be enhanced if the client obtainsaccess to lower level signaling (e.g., transport level signaling, RRClevel signaling, etc.) and/or to events that happen within the accessnetwork.

A QoE monitoring and reporting framework of DASH may be provided. DASHmay rely on channel bandwidth estimation to be able to accomplish videorate adaptation. Such bandwidth estimation may be enhanced by thesignaling from lower layers (e.g., the transport layer, RRC layer,physical layer, etc.).

A client may be informed of access network events through signaling fromthe network. A client may estimate and/or infer network conditions viacross-layer mechanisms. A client may detect network events, for example,such as but not limited to congestion, mobility (e.g., inter-RAT,intra-RAT handovers), changes in state of a wireless channel, abruptchanges in received signal power, and/or the like.

A network element (e.g., an eNodeB) may indicate network congestion tothe client using signaling (e.g., explicit signaling). For example,Explicit Congestion Notification (ECN) may be utilized to inform theclient of network congestion. ECN may be an extension to TCP/IP that maybe used for signaling congestion without dropping packets. ECN may beused when the endpoints support the use of ECN. ECN may be effectivewhen supported by the underlying network. For example, when an eNodeBdetects a congestion scenario, ECN may set a Congestion Encountered (CE)flag bit and send it to a WTRU. Upon receiving the packet, the WTRU maydetect the presence of the CE flag for client rate adaptation. The ECNfeature may mandate the receiver to notify the sender of the congestionscenario. The ECN feature may not mandate the receiver to inform thesender, for example, because the rate adaptation mechanism may reside inthe WTRU. The DASH protocol may include guidelines for the processing ofECN bits in the DASH client, for example, such as to modify (e.g.,increase or decrease) the requested rate, issue a TCP reset, abort theHTTP request, etc.

Cross-layer signaling may be utilized by a WTRU, for example, to infercongestion, mobility events, and/or the state of the wireless channel.Cross-layer signaling may refer to signaling that occurs at layers otherthan the application layer. For example, from the perspective of a DASHclient, the cross-layer signaling may be information that may beavailable in layers other than the application layer. Cross-layersignaling may be leveraged to predict the occurrence of certain events,for example, such as, but not limited to network congestion and/or achange in state of a wireless channel that may occur due to mobility orhandovers for client rate adaptation. For example, physical layersignaling parameters such as, but not limited to Channel QualityIndicator (CQI), physical resource blocks (PRB) allocation, and/or RRCsignaling may be used to predict the occurrence of certain events, forexample, before they actually occur. Physical layer signaling parametersmay enable rate adaptation by the client.

The cross layer parameters that may be used by the client may be WTRUspecific. For example, it may not be necessary to perform cross layersignaling within the WTRU for rate adaptation. The WTRU may be made tointernally set the ECN bit, for example, if the WTRU infers of a networkcongestion situation by means other than eNodeB signaling. The DASHclient may include guidelines for the processing of cross-layersignaling in the DASH client, for example, to lower the requested rate,issue a TCP reset, abort the HTTP request, etc. For video telephony, IMSmay specify the handling of the ECN bit. For networks which do notsupport the ECN bit, cross-layer signaling in the WTRU indicatingnetwork conditions may be used for rate adaptation.

One or more embodiments described herein may relate to, for example,packet-loss detection and prevention of loss propagation in wirelessvideo telephony, smooth stream switching for MPEG/3GPP DASH,multi-hypothesis rate adaptation for a DASH-client, and/or architectureof a DASH streaming client.

FIG. 2 is a diagram that illustrates an example of a wireless systemwith a DASH streaming client. In the example system 200, a WTRU 202 maystream multimedia data serviced by a network element (e.g., an eNodeB(eNB) 204) over an air interface 206. Multimedia content may be encodedat different rates, for example, as illustrated in block diagram 220.The multimedia content may reside in the HTTP server 210. The WTRU 202may include a pull-based video streaming client. For example, the WTRU202 may include a DASH client. The WTRU 202 may play a central role inrate adaptation. For example, the WTRU 202 may estimate and/or predictthe available bandwidth of the communication channel. The WTRU mayrequest media segments encoded at data rates according to the estimatedand/or predicted communication channel. For example, graph 240illustrates an example of a WTRU requesting media segments encoded atdifferent data rates based on changing channel conditions. The clientmay determine one or more conditions associated with the access network,for example, the congestion of the network, mobility events, and/or thestate of the wireless channel. For example, the WTRU 202 may receivesignaling from other layers relating to network events and/or conditionsassociated with the communication channel. The WTRU may estimate and/orpredict network events and/or conditions associated with thecommunication channel. The client request and/or receive (e.g., stream)video at a rate that is commensurate with what the channel is expectedand/or predicted to support.

The potential impact on throughput and latency of congestion in theaccess network, mobility events, and/or the state of the wirelesschannel may be signaled to a client, for example, before the clientapplication would be able to discover them on its own by monitoringtransport layer statistics. Early indications of rate or latency changesmay provide a better QoE.

DASH rate adaptation may be described herein. For example, a networkelement (e.g., an eNodeB) may signal a congestion encountered situationby setting the Congestion Encountered (CE) bit, which may be part of theECN field. The network element may send the ECN field including the CEbit to a WTRU. The WTRU may use the presence of CE bit information forDASH rate adaptation, for example, as described herein.

Cross-layer parameter(s) may be utilized by a WTRU for rate adaption.For example, congestion, mobility, and/or the state of the wirelesschannel may be inferred using one or more cross-layer parameters (e.g.,physical layer parameters, RRC layer parameters, MAC layer parameters,etc.). One or more cross-layer parameters may be utilized with theamount of requested data that the WTRU (e.g., DASH client) has not yetreceived. For example, the amount of requested data that the WTRU hasnot received may be used by the WTRU as a cue to estimate the channelconditions. The WTRU may identify statistics associated with the amountof data received and requested by the WTRU to estimate the channelconditions. RRC signaling may be leveraged by a WTRU for DASH rateadaptation. Cross-layer signaling may be used for IMS based videotelephony rate adaptation in networks which do not support explicit ECNsignaling.

Network signaling using the Explicit Congestion Notification (ECN) fieldmay be provided. The ECN field may be an element of TCP/IP that may beused for signaling congestion without dropping packets. The ECN fieldmay be used when the endpoints support and/or use it. The ECN field maybe effective when supported by the underlying network. The use of theECN field may allow the WTRU to not have to echo back the congestionindication to the sender.

FIGS. 3A-B are diagrams illustrating example methods of ECN usage. FIG.3A is a diagram illustrating an example method of ECN usage where an IPpacket may be transmitted from a network element (e.g., a server). Indiagram 300, the IP packet 302 may initially have an ECN flag 304 set to10. This may mean that it is an ECN capable transport. When the packetreaches a router or intermediate gateway 306, the packet 302 mayencounter congestion and the ECN flag 304 may be set to 11. This maymean that congestion may have been encountered. When congestion isencountered, the CE bit may be set to 1. Upon receiving the IP packet302 with the CE bit, the receiver 308 (e.g., WTRU, the DASH client,etc.) may echo back the congestion indication to the sender (e.g., theserver 310) with the ECN-Echo (ECE) bit set 312.

FIG. 3B is a diagram illustrating an example method for ECN usage. Forexample, as shown in diagram 320, rate adaptation may be performed at areceiver 328, for example, a WTRU (e.g., a DASH client residing on aWTRU). Since rate adaptation may be performed at the receiver 320 (e.g.,the client), there may be no need to send the ECN-Echo (ECE) indicationback to the sender. The receiver 328 may perform rate adaption uponreceiving the ECN field 324 (e.g., with the CE bit set to 1) of the IPpacket 322 from the sender (e.g., server 330), for example, via a routeror intermediate gateway 326.

The ECN flag may be used by the client for rate adaption. For example,when a network element (e.g., an eNodeB, router, etc.) detects acongestion situation, the network element may set the CE bit and maytransmit the CE bit to the W 1′RU. Mobility events and/or channelconditions may indicate loss (e.g., incipient loss) of throughput. Thenetwork element may detect the presence of congestion and/or send theECN field with the CE bit set to the WTRU. For example, a networkelement may detect the presence of congestion due in part to a number ofWTRUs that the network element is serving, and/or the buffer occupancyand/or QoS that the network element may meet (e.g., simultaneously meet)for the WTRUs. The WTRU may perform rate adaption upon receiving apacket with the CE bit set. For example, the WTRU may pass the CE bit toa rate adaptation module of a DASH client residing on the WTRU.

FIG. 4 is a diagram illustrating an example of an ECN bit that may beset by a network element (e.g., an eNodeB) and used by a WTRU for rateadaptation. The diagram 400 may be from a protocol stack perspective. Anetwork element 402 (e.g., an eNodeB) may be configured to detectcongestion on a communication channel 406 between it and a WTRU 404. Thenetwork element 402 may be configured to set a CE bit of the ECN fieldto indicate the presence of network congestion. The network element 402may transmit the CE bit to the WTRU 404. The WTRU 404 may receive the CEbit. The WTRU 404 may pass the CE bit up to the application layer, forexample, to a DASH client residing at the application layer of the WTRU404. The DASH client may interpret the CE bit and perform rate adaptionaccordingly.

FIG. 5 is a flow diagram illustrating an example procedure for a networkelement (e.g., an eNodeB, router, gateway, etc.) to set the ECN bit andfor the WTRU (e.g., a DASH client residing on the WTRU) to perform rateadaptation. In the procedure 500, the network element may receive an IPpacket at 502. At 504, the network element may determine whether or notcongestion is detected. If network congestion is detected, then thenetwork element may set the CE bit of the ECN field, for example, sothat the ECN field is set to 11. At 508, the network element performsone or more routing functions (e.g., pass the IP packet down theprotocol stack). At 510, the network element transmits the IP packet tothe data link layer. At 512, the network element may transmit the IPpacket.

At 514, the WTRU may receive the IP packet, for example, via the datalink layer. At 516, the WTRU may perform one or more routing functions(e.g., pass the IP packet up the protocol stack to the applicationlayer). At 518, the WTRU may determine whether the ECN field of the IPpacket is set to 11. If not, then the WTRU may perform other processingat 520. If the ECN field of the IP packet is set to 11, then the WTRUmay determine whether the protocol type is TCP at 522. If the protocoltype is not TCP then the WTRU may perform other processing at 524. Ifthe protocol type is TCP, then the WTRU may determine whether the portnumbers correspond to a DASH session at 526. If not, then the WTRU mayperform other processing at 528. If the port numbers do correspond to aDASH session, then the WTRU may set the ECE flag in the TCP header to 1at 530. At 532, the WTRU, for example, the DASH client, may read the ECEflag and perform rate adaption accordingly.

Rate adaptation using physical layer parameters may be described herein.If ECN is not supported by the network, a WTRU (e.g., a client) mayperform rate adaptation using a physical layer parameter(s) and/or a MAClayer parameter(s), for example, a Channel Quality Indicator (CQI), anumber of Physical Resource Blocks (PRBs) assigned to the WTRU, and/oran amount of requested data that has not yet been delivered to the WTRU(e.g., an application residing on the WTRU). A WTRU may have access to aCQI. For example, the WTRU may generate the CQI and/or the number ofPRBs that it has been allocated. The WTRU may generate the CQI and/orthe number of PRBs that it has been allocated by monitoring a physicaldownlink control channel (PDCCH).

A WTRU (e.g., a client) may calculate the estimated physical layerthroughput obtained over a time scale of interest. For example, t_(dash)may represent the time interval between two successive requests of theWTRU (e.g., ‘HTTP GET’ requests) for rate adaptation. The WTRU maymonitor the trend of the estimated physical layer throughput (e.g.,using the CQI and/or the allocated PRBs) over a time scale that issmaller than t_(dash), for example, together with the amount of datathat the WTRU may have requested (e.g., the amount of data that theclient requested may be obtained from the segment size) to estimate thecongestion level of the network and/or weak downlink conditions.

FIG. 6 is a diagram illustrating an example of a timeline for clientrate adaptation and estimated throughput. Graph 600 is an exampletimeline that illustrates the time between HTTP GET requests of a WTRU.For example, if the WTRU (e.g., client) issues a HTTP GET request attime T₁, then the next request from the WTRU may go out at T₁+t_(dash).The segment size of HTTP GET request may be larger than a requestedsegment size. For example, whenever the client issues a request ofsegment size, there may be enough data in the transmit buffer in thenetwork element (e.g., eNodeB) for the WTRU.

The WTRU may estimate the throughput of the channel. For example, theestimated throughput over a time duration of

${t_{e} = {\left( \frac{1}{N} \right)t_{dash}}},$

where N may be chosen such that it is neither small, nor large (e.g., Nmay signify the granularity level with which the physical layerthroughputs may be estimated) may be calculated. The physical layerthroughputs may be estimated at times: T₁, T₁+t_(e), T₁+2 t_(e), . . .T₁+(N−1) t_(e).

The trend in estimated throughputs obtained may be observed and utilizedby a WTRU to estimate channel throughout. If there is a decreasing trendin the estimated throughput (e.g., due to network congestion and/or dueto weak downlink conditions, since the WTRU may have requested enoughdata at time T₁) during time interval [(T₁+(N−4)t_(e)),(T₁+(N−2)t_(e))], then the WTRU (e.g., DASH client) may determine theappropriate rate adaptation before it requests new rates at timeT₁+t_(dash). By looking at the physical layer throughputs (e.g., whichmay be indicative of the application layer throughput) at a finergranularity than what may be observed by the client application, theWTRU (e.g., client) may determine potential network congestion and/orweak channel conditions, for example, before the client sends out a newrequest.

The estimated throughout over time interval t_(e) may be determined, forexample, as provided herein. nPRB may be the total number of physicalresource blocks that carry WTRU data. RB_(i) may denote the i^(th)physical resource block. CQI_(i) may be the Channel Quality Indicator inPRB_(i). TBS may represent a vector of transport block size thatcorresponds to possible CQI. For example, in LTE there may be 28possible CQI values and a transport block size may correspond to eachCQI. TBS(CQI_(i)) may represents the transport block size correspondingto CQI_(i). The estimated throughput over a time interval t_(e) may be:

${{Estimated}\mspace{14mu} {throughput}} = {\left( \frac{1}{t_{e}} \right){\sum\limits_{i}^{nPRB}\; {{TBS}\; \left( {CQI}_{i} \right)}}}$

RRC signaling may be used by a WTRU to perform rate adaptation. RRCsignaling may occur between the WTRU and the network element, forexample, where the WTRU may report the status of mobility, receivedsignal power, weak downlink conditions to the network, and/or the like.RRC signaling may be used to predict the occurrence of an event (e.g.,from the measurement report message (MRM)) that the WTRU may signal to anetwork element (e.g., an eNodeB). The MRM may be fed back to the DASHrate adaptation module. An example of may be provided FIG. 7.

FIG. 7 is a diagram illustrating an example of cross-layer DASH rateadaptation. The diagram 700 may be from a protocol stack perspective. Anetwork element 702 (e.g., an eNodeB) may be in communication with aWTRU 704. The WTRU may determine (e.g., measure and/or estimate) networkconditions. The WTRU 704 may include a DASH client, which may, forexample, reside at the application layer of the WTRU 704. The WTRU mayperform rate adaption, for example, as described herein. For example,the DASH client residing at the application layer of the WTRU mayperform rate adaption. For example, rate adaption may be performed basedon one or more cross-layer (e.g., lower layer) parameters, such as, butnot limited to network layer parameters, RRC layer parameters, RLC layerparameters, MAC layer parameters, physical layer parameters, transportlayer parameters, or the like.

The WTRU 704 may be connected to a cellular network. The WTRU 704 mayencounter a cell change event, such as a mobility event, for example.The change cell event may trigger the WTRU 704 to perform rate adaption.For example, the WTRU 704 may be streaming video while connected to anLTE/LTE-Advanced cell. Due to network coverage and/or WTRU mobility,conditions may necessitate that the WTRU 704 hands over to 3G or 2G. Thehand over from LTE to 3G/2G, (e.g., or from 3G to 2G; e.g., from ahigher to lower capability access technology) may have a detrimentaleffect on video streaming due to decrease in capacity. While handovermay provide a short term boost in throughput, handover from LTE to 2G/3Gmay lower the peak achievable throughput. The effect of video streamingmay suffer the greatest during the handover (e.g., when the handover isin progress) when the DASH client has not yet adapted to the network.

A WTRU may deliver a Measurement Report Message (MRM) to the networkelement (e.g., eNodeB), for example, in response to measurement controlmessages that are sent by the network element to the WTRU. The MRM maybe fed to the DASH client (e.g., DASH rate adaptation module) residingon the WTRU, for example, before the handover process is initiated.

The WTRU may perform rate adaption during a cell change event, such as ahandover, for example. For example, for 3G to 2G handover, the MRMs thatmay be used as events before a 3G to a 2G handover and which may besignaled to the DASH client for rate adaptation may comprise, event 3c,event 2d, and event 3a. For event 3c, the estimated quality of the othersystem's frequency may be above a threshold. For event 2d, the estimatedquality of the currently used frequency may be below a threshold. Forevent 3a, the estimated quality of the currently used UTRAN frequencymay be below a threshold and the estimated quality of the other system'sfrequency may be above a threshold.

FIG. 8 is a diagram illustrating an example use of RRC signaling forclient rate adaptation. The diagram 800 may include a WTRU 802 that maybe in communication with a source 804, which may be in communicationwith a target 806. The WTRU 802 may perform rate adaption during a cellchange event, for example, as described herein. The WTRU 802 may be incommunication with the source 804. The source 804 may be incommunication with the target 806. The WTRU may change cells from a cellof the source 804 to a cell of the target 806, for example, due tomobility, network congestion, and/or the like. The source 804 and/or thenetwork element may be a network element (e.g., eNodeB, router, gateway,or the like). The source 804 and/or the target 806 may refer to cells.The source 804 and the target 806 may be two cells that are part of thesame network element (e.g., eNodeB) or different network elements.

A DASH rate adaptation module may reside in the WRTU 802. A handovercommand (“HO command” in diagram 800) may be issued at the end of theprocess by the source 804 to the WTRU 802. One or more events notillustrated may occur before the HO command is received by the WTRU 802.For example, the source 804 may transmit a Measurement Control Messageto the WTRU 802. The WTRU 802 may transmit Event 2D (e2d) and/or Event3A/Event B2 (e3a/eB2) to the source 804. This source 804 may determineto handover the WTRU 802 to the target 806. The source 804 may transmita HO request to the target 806. The target 806 may transmit a HOacknowledgement to the source 804. The source 804 may transmit a HOcommand to the WTRU 802. As such, the WTRU 802 may be handed over to thetarget 806.

The call flow of diagram 800 (e.g., partially or in its entirety) may beused to perform rate adaptation. For example, rate adaption may beginwhen the WTRU receives e3a, for example, because the quality of the usedfrequency may be below a certain threshold, the quality of targetsystem's frequency may be above a certain threshold, or the like.Signaling that indicates that a cell/handover may be imminent may beused to perform rate adaption, for example, before the cell/handoveractually occurs. For example, signaling that indicates that acell/handover may be imminent may indicate a likely change in capacity,which may prompt the WTRU 802 to perform rate adaption. Performing rateadaption based on cross layer signaling (e.g., RRC signaling) may bequicker than the WTRU 802 waiting to receive the HO command and thenrelying on the transport protocol to initiate rate adaptation.

For an LTE 3G/2G handover, for example, event B1 may signify that aneighbor cell's radio link quality on a different RAT has become betterthan a threshold. Event B2 may signify that a serving cell radio qualityhas become worse than a threshold and/or the neighbor cell's radio linkquality on a different RAT has become better than a threshold. Ahandover command may be issued by the network element (e.g., eNodeB)after one or more events are reported by the WTRU. The events may be fedback to signal a decrease in capacity, for example, that may be causedby the handover to the DASH client before the handover command is issuedby the network element to the WTRU. For example, once e3a is triggeredby the WTRU, the WTRU may perform rate adaption. For example, the DASHclient rate adaptation module of the WTRU may be informed that e3a istriggered and perform rate adaption accordingly. Even if e3a istriggered, the network element may not be able to handover, for example,due to cell loading, admission control, etc. The RRC signaling messagesthat the serving network element issues and/or that the WTRU triggersmay be followed based on the serving cell conditions, and the clientrate may be adapted accordingly (e.g. without causing any detrimentaleffect).

A WTRU may perform rate adaption in response to receiving a weak cellindication. The WTRU may receive events that may be indicative of a weakcell (e.g., weak signal strength received from the cell or the like).For example, one or more events may be fed back to the WTRU. The eventsmay occur before packet errors that might occur due to the signalstrength from the serving cell falling below a threshold. Event A2,event 1f, and event 2d may be MRMs that may be used by a WTRU for rateadaptation. For event A2 (e.g., Intra-frequency reporting in LTE), theserving cell radio link quality may become worse than a threshold. Forevent 1f (e.g., Intra-frequency reporting event in 3G), a primary CPICHmay become worse than a threshold. For event 2d (e.g., Inter-frequencyreporting event in 3G), the estimated quality of the currently usedfrequency may be below a threshold. The events may be proactively fedback to the WTRU to signal a likelihood of impending poor downlinkconditions, which may cause packet losses. The WTRU (e.g., a DASH clientrate adaptation module) may receive the events prior to an actualthroughput decrease. The WTRU may perform rate adaption before anydecrease in throughout.

A WTRU may perform rate adaption as described herein. The WTRU mayinclude an adaptive bitrate client, such as a DASH client, for example,residing at the application layer of the WTRU. For example, the WTRU mayinclude a rate adaption module of a DASH client that resides on theWTRU. The WTRU may receive an encoded data stream. The data stream maybe a video stream, for example. The data stream may be a multi-rateencoded data stream. For example, the data stream may be encodedaccording to a Dynamic Adaptive HTTP Streaming (DASH) standard. The WTRUmay request and/or receive the data stream encoded at a first rate. Forexample, the WTRU may request and/or receive (e.g., indirectly receive)the data stream from a content server, such as a HTTP content server, orthe like.

The WTRU may perform rate adaption, for example, according a cross-layerparameter and/or a congestion encountered (CE) bit. Rate adaption may beperformed at the application layer of the WTRU. For example, rateadaption may refer to a process of determining to request the datastream encoded at a different rate based on one or more variables, suchas the channel conditions. For example, a DASH adaption rate module ofthe WTRU may perform the rate adaption for the encoded video stream. Forexample, rate adaption may include requesting the data stream encoded ata different rate, issuing TCP reset associated with the data stream,and/or aborting an HTTP request for the data stream. The WTRU (e.g.,DASH client) may include guidelines for performing rate adaptation,whereby the cross-layer parameter(s) may be used to determine whether ornot the WTRU should perform rate adaptation.

The WTRU may monitor and/or receive a cross-layer parameter. Across-layer parameter may be any parameters (e.g., signaling) that isdirected to a layer of the WTRU other than the application layer. Forexample, the cross-layer parameter may be a physical layer parameter, aRRC layer parameter, and/or a MAC layer parameter. For example, thecross-layer parameters may be a CQI, a PRB allocation, a MRM, or thelike.

The WTRU may perform rate adaption based on the cross-layer parameter.For example, the WTRU may set the CE bit of an Explicit CongestionNotification (ECN) field based on the cross-layer parameter. The WTRUmay set and/or receive a CE bit of an ECN field based on the cross-layerparameter. The WTRU may predict (e.g., estimate) one or more of networkcongestion, throughout of the communication channel, a cell change event(e.g., a mobility event), and/or a channel condition that indicates lossof throughput using the cross-layer parameter. For example, the WTRU maydetermine to request the data stream encoded at a second rate based onone or more of the cross-layer parameter, the CE bit, and/or theprediction based on the cross-layer parameter. The second rate may belower than the first rate or the second rate may be higher than thefirst rate. The WTRU may receive the data stream encoded at the secondrate.

The WTRU may receive a data stream. The date stream may be encoded at afirst rate. The WTRU may receive a congestion encountered (CE) bit. TheCE bit may be part of an ECN field. The ECN field may be received from anetwork element, such as a router, eNodeB, gateway, or the like. TheWTRU may receive the CE bit upon a network element detecting one or moreof a congestion scenario, a cell change event (e.g., a mobility event),and/or a channel condition that indicates loss of throughput.

The WTRU may determine to request the data stream encoded at a secondrate based on the CE bit. The WTRU may not transmit an ECN-Echo (ECE)bit set to a sender after receiving the CE bit. The second rate may belower than the first rate or may be higher than the first rate. The WTRUmay request the data stream encoded at the second rate, for example,from a content server. The WTRU may receive the data stream encoded atthe second rate from a content server.

The WTRU may receive the data stream encoded at the first rate. The WTRUmay monitor a PDCCH and determine a physical layer parameter based onthe PDCCH. For example, the physical layer parameter may include a CQI,a PRB allocation, or the like. The WTRU may determine to request thedata stream encoded at a different rate based on the physical layerparameter. For example, the WTRU may set the CE bit of an ECN fieldbased on the physical layer parameters, and determine to request thedata stream encoded at the different rate based on the CE bit. The WTRUmay request and/or receive the data stream encoded at a different rate.

The available bandwidth of a communication channel may be estimated by aWTRU (e.g., a DASH client) to reduce the estimation error. FIG. 9 is adiagram illustrating an example of TCP congestion window size behaviorvs. time. The diagram 900 may illustrate how the congestion window sizeevolves in a typical TCP connection. For example, the TCP throughput maybe approximately equal to (¾)W*MSS/RTT, where W may be the congestionwindow size in Maximum Segment Size (MSS) and RTT may be the round triptime. When in the congestion avoidance phase, the congestion window sizemay increase by 1 MSS every RTT. If there is an abrupt change in theavailable bandwidth, then it may take TCP Win/2 RTTs to learn the newbandwidth, where Wm may be the maximum congestion window size.

If other means are used to inform the WTRU (e.g., the DASH Client) ofthe changes in the available bandwidth, the delay in the DASH rateadaptation may be reduced. For example, if ECN is used at the basestation, then the delay may be reduced to approximately the order of 1RTT. For example, if physical layer information collected at the WTRU isused, the delay may be reduced to approximately the order of 1 TTI.

FIG. 10 is a diagram illustrating example timing of HTTP GET requestsand available bandwidth vs. time. The diagram 1000 may illustrate anexample timing of HTTP GET request. The diagram 1010 may illustrate anexample timing of the available bandwidth vs. time, for example, withrespect to the HTTP GET requests of diagram 1000. For example, the timeinterval between consecutive HTTP GET requests may be T sec. Theavailable bandwidth may drop at time t+s sec, due to, for example,handover or shadowing. If T−s is shorter than (Wm/2)*RTT, then TCP maynot be able to accurately estimate the new available bandwidth, and mayrequest a media segment of a high rate. This may increase theprobability of rebuffering. If T−s is longer than (Wm/2)*RTT, then TCPmay be able to learn the new available bandwidth accurately.

For example, the old available bandwidth may be R1, the new availablebandwidth may be R2, and R2=αR1, where 0<α<1. The maximum congestionwindow sizes may be Wm1 and Wm2, respectively. Then, Wm2=αWm1.

FIG. 11 is a diagram 1100 that illustrates an example of the estimatedavailable bandwidth by TCP as a function of time. The average inaccuracyof TCP's available bandwidth estimation may be calculated by a WTRU(e.g., a client residing on the WTRU). Assuming that t+s may beuniformly distributed in the time interval [t, t+T], the averageestimation error for TCP (where x=T−s) may be:

$\begin{matrix}{{E\;\left\lbrack {error}_{TCP} \right\rbrack} = {\int_{0}^{{(\frac{W_{m\; 2}}{2})}{RTT}}{\frac{1}{T}\frac{3}{4\; {RTT}}\left( {W_{m\; 1} - W_{m\; 2}} \right){{MSS}\left( {1 - \frac{x}{\left( \frac{W_{m\; 2}}{2} \right){RTT}}} \right)}\ {x}}}} \\{= {\frac{{\alpha \left( {1 - \alpha} \right)}W_{m\; 1}{RTT}}{4\; T}R_{1}}}\end{matrix}$

The WTRU may estimate the available bandwidth, and may use the estimatedavailable bandwidth to perform rate adaption. For example, the time thatit takes for the WTRU to estimate the available bandwidth may be U. Theaverage estimation error for an estimation implementation may be:

${E\;\lbrack{error}\rbrack} = {\frac{\left( {1 - \alpha} \right)U}{2\; T}R_{1}}$

If U<(W_(m2)/2)RTT, then the estimation implementation described hereinmay have better accuracy than the estimation error for TCP. For example,Wm2=20, RTT=300 ms, and MSS=512 bytes. This may correspond to an averagethroughput of 204.8 kbps. For example, U=500 TTIs. Then,U/((W_(m2)/2)RTT)=1/6. The estimation error may be reduced by a factorof 6 using the estimation implementation described herein.

The processes described above may be implemented in a computer program,software, and/or firmware incorporated in a computer-readable medium forexecution by a computer and/or processor. Examples of computer-readablemedia include, but are not limited to, electronic signals (transmittedover wired and/or wireless connections) and/or computer-readable storagemedia. Examples of computer-readable storage media include, but are notlimited to, a read only memory (ROM), a random access memory (RAM), aregister, cache memory, semiconductor memory devices, magnetic mediasuch as, but not limited to, internal hard disks and removable disks,magneto-optical media, and/or optical media such as CD-ROM disks, and/ordigital versatile disks (DVDs). A processor in association with softwaremay be used to implement a radio frequency transceiver for use in aWTRU, WTRU, terminal, base station, RNC, and/or any host computer.

1-20. (canceled)
 21. A wireless transmit/receive unit (WTRU) configuredto perform rate adaption, the WTRU comprising: a processor configuredto: receive a data stream encoded at a first rate; set a congestionencountered (CE) bit of an Explicit Congestion Notification (ECN) fieldbased on a cross-layer parameter; determine to request the data streamencoded at a second rate based on the CE bit; and request the datastream encoded at the second rate.
 22. The WTRU of claim 21, wherein thedetermination to request the data stream encoded at the second ratebased on the CE bit is performed at an application layer of the WTRU.23. The WTRU of claim 21, wherein the processor is further configuredto: predict a change in throughput using the cross-layer parameter; anddetermine to request the data stream encoded at the second rate based onthe prediction.
 24. The WTRU of claim 21, wherein the cross-layerparameter is a physical layer parameter, and the processor is furtherconfigured to: monitor a physical downlink control channel (PDCCH); anddetermine the physical layer parameter by monitoring the PDCCH.
 25. TheWTRU of claim 21, wherein the cross-layer parameter is a physical layerparameter, a Radio Resource Control (RRC) layer parameter, or a MediaAccess Control (MAC) layer parameter.
 26. The WTRU of claim 21, whereinthe cross-layer parameter is a Channel Quality Indicator (CQI).
 27. TheWTRU of claim 21, wherein the cross-layer parameter is a physicalresource block (PRB) allocation.
 28. The WTRU of claim 21, wherein thecross-layer parameter is a measurement report message (MRM).
 29. TheWTRU of claim 21, wherein the cross-layer parameter is an amount ofrequested data that has not been received by the WTRU.
 30. The WTRU ofclaim 21, wherein the data stream is encoded according to a DynamicAdaptive HTTP Streaming (DASH) standard.
 31. A method of performing rateadaptation with a wireless transmit/receive unit (WTRU), the methodcomprising: receiving a data stream encoded at a first rate; receiving across-layer parameter; predicting a change in throughput using thecross-layer parameter; determining to request the data stream encoded ata second rate based on the prediction; and requesting the data streamencoded at the second rate.
 32. The method of claim 31, wherein thecross-layer parameter is a physical layer parameter, the method furthercomprising: monitoring a physical downlink control channel (PDCCH); anddetermining the physical layer parameter by monitoring the PDCCH. 33.The method of claim 31, wherein the cross-layer parameter is a physicallayer parameter, a Radio Resource Control (RRC) layer parameter, or aMedia Access Control (MAC) layer parameter.
 34. The method of claim 31,wherein the cross-layer parameter is a Channel Quality Indicator (CQI).35. The method of claim 31, wherein the cross-layer parameter is aphysical resource block (PRB) allocation.
 36. The method of claim 31,wherein the cross-layer parameter is a measurement report message (MRM).37. The method of claim 31, wherein the cross-layer parameter is anamount of requested data that has not been received by the WTRU.
 38. Themethod of claim 31, wherein the data stream is encoded according to aDynamic Adaptive HTTP Streaming (DASH) standard.
 39. A method ofperforming rate adaptation with a wireless transmit/receive unit (WTRU),the method comprising: receiving a data stream encoded at a first rate,the data stream being encoded according to a Dynamic Adaptive HTTPStreaming (DASH) standard; receiving a cross-layer parameter;determining to request the data stream encoded at a second rate based onthe cross-layer parameter, the second rate being less than the firstrate; and requesting the data stream encoded at the second rate.
 40. Themethod of claim 39, wherein the cross-layer parameter is a physicallayer parameter, the method further comprising: monitoring a physicaldownlink control channel (PDCCH); and determining the physical layerparameter by monitoring the PDCCH.
 41. The method of claim 39, whereinthe cross-layer parameter is a physical layer parameter, a RadioResource Control (RRC) layer parameter, or a Media Access Control (MAC)layer parameter.
 42. The method of claim 39, wherein the cross-layerparameter is a Channel Quality Indicator (CQI).
 43. The method of claim39, wherein the cross-layer parameter is a physical resource block (PRB)allocation.
 44. The method of claim 39, wherein the cross-layerparameter is a measurement report message (MRM).
 45. The method of claim39, wherein the cross-layer parameter is an amount of requested datathat has not been received by the WTRU.
 46. The method of claim 39,further comprising: receiving a congestion encountered (CE) bit of anExplicit Congestion Notification (ECN) field; and determining to requestthe data stream encoded at a second rate based on the CE bit.
 47. Themethod of claim 46, wherein the data stream encoded at the first ratecomprises the CE bit of the ECN field.
 48. The method of claim 39,further comprising: predicting a change in throughput using thecross-layer parameter; and determining to request the data streamencoded at a second rate based on the prediction.